The formula is faulty. Your gonna get I higher number if you increase your amps. That can't work. Basically you dont have enough info either. You will need to calculate the volts too. For instance the more volts or higher cell count you use, the less amps you will draw. So say you fly a 3lb heli and are drawing 40A on 6S. On 12S you would draw like 25A. So on 6S you will get 5min for 2000mah. On 12S you will get 10min for 2000mah. All numbers are fictional just to show how it works. So basically Volts = power Mah = capasity.